Interesting model D / Voyager comparision

Tips and techniques for Minimoog Analog Synthesizers
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MC
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Interesting model D / Voyager comparision

Post by MC » Sat May 29, 2010 7:38 pm

It has been known that the model D with the filter wide open possesses a top end sheen that the Voyager is lacking.

I confirmed this with my own set. I have an early RA Moog Minimoog and the resonant color between that and the Voyager are close - until you open the filter all the way.

Today, I routed the Voyager VCOs - via the MIXER IN/OUT jack - to the EXT IN of the model D. The MIXER OUT taps the VCOs *before* the filters so the model D gets the unprocessed Voyager VCO audio. I also opened the Voyager filters all the way so I could do a quick A/B by unplugging the insert cable in the MIXER IN/OUT jack.

First test was to see how well the Voyager matches the model D waveforms. This was really easy to A/B using the rocker switches on the mixer of the D.

Ramp was radically different, I couldn't dial the waveshape the match the model D. Now the 3rd VCO on the D has both rising and falling ramp, the other two have falling ramp only which I couldn't match. So I tried the model D 3rd oscillator rising ramp and WHAMMO that matches the Voyager.

Voyager has rising ramp, almost every model D ramp patch uses FALLING ramp. That accounts for part of the sonic difference. Small wonder that model D owners dial up a ramp lead and complain that the Voyager doesn't sound their model D - now we know why!

Triangle, ramp/tri, and 50% pulse were easy to match. I could not quite match the 35% and 15% pulse of the D, difference wasn't as dramatic as the ramps. One also has to be careful not to dial the model D level too high as this will introduce subtle distortion - the model D mixer->VCF->VCA can overdrive if desired. Distortion can throw off the comparision and I wanted to eliminate that variable.

So now that I know which waveforms can be matched, I dialed up 50% pulse on both units. With all audio going through the D, pretty consistent. Then I unplugged the insert on the Voyager which reverted the Voyager audio back to the Voyager.

The difference was SHOCKING. With Voyager audio going through the D, the Voyager had taken on the timbre of the model D and now had that top end sheen. Unplug the insert cable, radical sound difference. This is NOT a joke. Anybody with possession of both should repeat this test for themselves.

So.... why? The likely culprit is the model D VCAs. I put less emphasis on the filter because both have all matched transistor pairs (my RA Moog has all matched pairs, later models D only matched the top and bottom pairs) and the resonant color is pretty close. Why the VCA? The model D VCA is a simple discrete differential amplifier - right out of a textbook. The Voyager VCA is a 13700 OTA.

Now the 13700 OTA can be configured as a high fidelity device. The discrete VCA in the model D are not high fidelity. Also the discrete VCA can be overdriven mildly which sounds pleasant. In fact, the model D has TWO of these VCAs, the second one is tied to the rear panel LOUDNESS jack for external VCA control (such as volume pedal). 13700 can be linear, but the BJT transistors in the discrete VCA won't be linear. It takes multiple stages of BJT transistors to get them linear. Non-linear response will alter the frequency response of the discrete VCA, which makes it sound "dirty". And the model D audio is processed by TWO of these "dirty" discrete VCAs. So the sonic differences are due to the frequency responses between the 13700 and the discrete VCAs, and also to the mild overdrive of the discrete VCAs.
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EricK
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Re: Interesting model D / Voyager comparision

Post by EricK » Sat May 29, 2010 9:15 pm

Of all of the countless threads and ensuing flame wars that have srpung up on this subject matter, this is probably the most definitive post on the subject of Voyager vs D out there.

Thanks MC

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Re: Interesting model D / Voyager comparision

Post by LivePsy » Sat May 29, 2010 9:27 pm

MC, that really is shocking. I've been blaming the slow rise times of the Voyager waveforms for that lack of sheen. But if it gets the Mini top end just by putting the raw Voyager waveforms through to the Mini mixer, well, then its the Voyager filter/vca path taking a little sheen off. Of course, the opposite could be true: the Mini might be adding desirable dirt.

You can actually raise the Voyager filter cutoff a little higher than the cutoff knob determines. Put a constant voltage into the external filter cutoff input - the CP-251 is essential for these toolbox tricks. It gets part way closer to a Mini. I'm not a purist by any means BTW. I don't have a Mini, but there's a brightness from vinyl records which isn't quite there on a Voyager. And I think this is the reason for the flame wars about Mini vs Voyager. The Mini isn't perfection, but it can have a sound which the Voyager doesn't quite achieve.

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latigid on
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Re: Interesting model D / Voyager comparision

Post by latigid on » Sat May 29, 2010 9:37 pm

I think this is spot on, it really shows the difference a) old parts (far tolerance) and b) discrete vs IC designs.

It's why old synths have "that sound", raw and energetic. It really is the non-linearity of analog which makes it so, and also makes it difficult to model. Unpredictable overdrive stages and in-circuit coupling (e.g. Taurus).

Thanks MC!

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Re: Interesting model D / Voyager comparision

Post by machinea » Sun May 30, 2010 2:00 am

interesting read thank you... What I've learned is:

I need a cp251 to add to my voyager and I should probably just be on the look out for a model D while I'm at it.
I love these synths. I have never assumed the voyager was a remake of the model d but rather a tribute to it but different in its own right.

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Re: Interesting model D / Voyager comparision

Post by MarkM » Mon May 31, 2010 11:00 am

Very interesting. Good experiment, MC.

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Re: Interesting model D / Voyager comparision

Post by psicolor » Mon May 31, 2010 1:57 pm

MC wrote:the model D with the filter wide open possesses a top end sheen that the Voyager is lacking. (...) Non-linear response will alter the frequency response of the discrete VCA, which makes it sound "dirty".


Do you think an overdrive could help reproducing the sound of the D with the Voyager?

Maybe an external VCA with non-linear response could make the Voyager sound like a D...?

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Re: Interesting model D / Voyager comparision

Post by moremagic » Mon May 31, 2010 11:04 pm

latigid on wrote:I think this is spot on, it really shows the difference a) old parts (far tolerance) and b) discrete vs IC designs.

I'm not sure the difference is in using an IC, but in using one with much more headroom than the old discrete circuit had.

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latigid on
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Re: Interesting model D / Voyager comparision

Post by latigid on » Tue Jun 01, 2010 12:10 am

Good point, perhaps I was thinking in terms of "equivalent circuit", e.g. like MC's comment of multiple transistors to get linear response etc., which would take up more board space than ICs..

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Re: Interesting model D / Voyager comparision

Post by ikazlar » Tue Jun 01, 2010 4:56 am

MC wrote:Ramp was radically different, I couldn't dial the waveshape the match the model D. Now the 3rd VCO on the D has both rising and falling ramp, the other two have falling ramp only which I couldn't match. So I tried the model D 3rd oscillator rising ramp and WHAMMO that matches the Voyager.


Radically different? I remember you did a waveform comparison between the Voyager and the Model D and while there is a small difference, I wouldn't say it's radical. So how come nearly identical down-sawtooth waveforms produce radically different spectra (as you say) and when you switch to ramp you can match the waveforms?
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Re: Interesting model D / Voyager comparision

Post by goldphinga » Tue Jun 01, 2010 5:17 am

I wonder if there could be a factory brightness mod sorted out for the LP and Voyager to get more top end out of them?
Last edited by goldphinga on Sun Oct 28, 2012 1:04 pm, edited 1 time in total.
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Re: Interesting model D / Voyager comparision

Post by sunny pedaal » Tue Jun 01, 2010 6:56 am

i own several moogs, always felt the voyager is closer to my beloved multimoog, soundways, then to my 2000serial model-D.
in every respect the model-d is more raw, meaty, whereas the multimoog is slightly more polished.
anyway i'll certainly repeat the test too, interesting

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Re: Interesting model D / Voyager comparision

Post by monokit » Tue Jun 01, 2010 7:05 am

Ok fine. So now, please, can we repeat the test with a Rudi Linhard (slewrate mod) modified Voyager (i have one)?

In case you wonder whats this slewrate mod is doing...have a listen:

Old Slewrate: http://share.ovi.com/media/noiseprofessor.public/noiseprofessor.10026
New Slewrate: http://share.ovi.com/media/noiseprofessor.public/noiseprofessor.10030

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MC
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Re: Interesting model D / Voyager comparision

Post by MC » Tue Jun 01, 2010 11:18 am

ikazlar wrote:
MC wrote:Ramp was radically different, I couldn't dial the waveshape the match the model D. Now the 3rd VCO on the D has both rising and falling ramp, the other two have falling ramp only which I couldn't match. So I tried the model D 3rd oscillator rising ramp and WHAMMO that matches the Voyager.


Radically different? I remember you did a waveform comparison between the Voyager and the Model D and while there is a small difference, I wouldn't say it's radical. So how come nearly identical down-sawtooth waveforms produce radically different spectra (as you say) and when you switch to ramp you can match the waveforms?


That initial comparision was with oscilloscope displays.

This time instead of using my eyes, I used my ears. The difference was very noticeable when you hear them side by side going through the same audio chain.
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Re: Interesting model D / Voyager comparision

Post by sunny pedaal » Tue Jun 01, 2010 12:11 pm

uhm, to be complete: my comparison of the sound of the voyager with the multimoog is meant for the slewratupgraded voyager ( had it modded 'bout a year ago , and agree it put more directness in the sound )
so : i think the (modded) voyager sounds more like a multimoog then as a minimoog. which is more than oke for me .

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